1. Field of the Invention
The present invention relates to an apparatus for adjusting a head gap between printing paper and a nozzle of a printing head in an inkjet printer, and more particularly, to an apparatus for automatically adjusting a head gap according to a change in thickness of printing paper in an inkjet printer.
2. Description of the Related Art
Generally, an inkjet printer, as shown in FIG. 1, includes a printing head 30 having a nozzle 31 at a lower part thereof to eject ink through the nozzle 31, a carrier 20 mounted with the printing head 30 therein, and a chassis 10 having a guide rail 11 and a carrier shaft 50 both guiding a movement of the carrier 20. At a rear part of the carrier 20, a supporting bracket 51 and a guide slider 22 are formed to allow the carrier 20 to be movable right and left along the carrier shaft 50 and the guide rail 11, respectively.
Thus, when printing paper 40 passes below a lower part of the printing head 30 through a paper-transporting roller 60 after being picked up from a paper-storing tray or a cassette by a pick-up roller (not shown), the printing head 30 mounted in the carrier 20 is moved right and left along the carrier shaft 50 and the guide rail 11 to perform a printing operation of ejecting the ink onto the printing paper 40 through the nozzle 31. Discharging rollers 70, 80 are disposed at a paper discharging portion of the inkjet printer.
However, in the inkjet printer, a distance or a head gap between the printing paper 40 and the nozzle 31 of the printing head 30 is generally fixed. Accordingly, when the inkjet printer prints an envelope or a postcard having a thickness of two or three times greater than that of general paper, the head gap is considerably reduced compared with that of when the general paper is printed, and the printing head 30 may be tilted with respect to the envelope or the post card. In this case, a spread or smear of the ink resulting in a problem of deterioration of a printing quality may be generated.
To solve the above problem, in the conventional inkjet printer, an apparatus 90 which can manually adjust the head gap between the printing paper 40 and the printing head 30 according to the thickness of the printing paper 40 is installed as shown in FIGS. 1 and 2. The apparatus 90 includes a carrier guide 21 formed in the guide slider 22 at an upper part of the carrier 20, a cam 23 having a cam surface mounted on the carrier to move the carrier 20 with respect to the chassis 10, a compression spring 24 biasing the carrier guide 21 to come in contact with the cam 23, and a spring guide 25 receiving and supporting the compression spring 24.
In operation, when the envelope, the postcard and the like are printed, the head gap is to be increased, and the cam 23 is rotated in a direction B by a user to push the carrier guide 21.
At this time, since the spring guide 25 is fixed to the carrier 20, the carrier guide 21 is biased in a direction D by a repulsive power of the compression spring 24. However, since the guide slider 22 elastically coupled to the carrier guide 21 is disposed not to be movable back and forth but to be slidable right and left along the guide rail 11, the guide slider 22 is not moved, but the spring guide 25 is backward pushed as much as the eccentricity of the cam surface of the cam 23.
As the spring guide 25 fixed to the carrier 20 is backward pushed, the carrier 20 mounted with the printing head 30 is rotated in a direction C about the carrier shaft 50. As a result, front parts of the carrier 20 and the nozzle 31 of the printing head 30 are rotated about the carrier shaft 50.
On the contrary, when the general paper is printed, the head gap is to be decreased, and the cam 23 is rotated in a reverse direction. As a result, the carrier 20 is rotated about the carrier shaft 50 and descended into the former position.
However, since in the conventional inkjet printer, the front part of the carrier 20 is ascended or descended to increase or decrease the head gap, there was a problem that the nozzle 31 of the printing head 30 is arranged to be tilted with respect to the printing paper 40. In this case, since there exists a difference in height between front and rear ends of the nozzle 31 a deflection or variation in the printing quality can occur at beginning and ending portions of the printing paper 40 which is printed by the nozzle 31.
Although the conventional inkjet printer may adjust the head gap with the above explained structure, to adjust t,he head gap, the user has to move the cam 23 whenever the kind of the printing paper 40 is changed, and consequently an operation error as well as inconvenience and troublesomeness may occur.
To improve these problems, as shown in FIG. 3, there has been proposed a method of ascending and descending a carrier 20xe2x80x2 by forming both ends 50xe2x80x3, 50xe2x80x2xe2x80x3 of a carrier shaft 50xe2x80x2 in the form of an eccentric cam having a given eccentricity xcex4 and then connecting the carrier shaft 50xe2x80x2 with a transmission (not shown) which is driven by a separate driving motor. However, since the method uses an additional driving motor and a transmission unit, a manufacturing cost increases, and an additional space for the driving motor and transmission is required, thereby resulting in an increase in size of the inkjet printer.
Therefore, it is an object of the present invention to provide an improved apparatus in an inkjet printer for adjusting a head gap between printing paper and a printing head according to a change in thickness of the printing paper.
It is another object to provide an improved apparatus in an inkjet printer for automatically adjusting a head gap between printing paper and a printing head by using only a driving force of a carrier driving motor and a paper-transporting roller driving motor without using a separate additional driving motor.
Additional objects and advantageous of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
These and other objects may be achieved, according to an embodiment of the present invention, by providing an apparatus for adjusting a gap between printing paper and a nozzle of a printing head ejecting ink on the printing paper in an inkjet printer. The apparatus includes a carrier mounted with the printing head, a chassis having a carrier shaft guiding a movement of the carrier, a carrier driving part moving the carrier right and left along the carrier shaft, a paper-transporting roller driving part driving a paper-transporting roller to transport the printing paper to be printed, a carrier ascent/descent part ascending and descending the carrier by rotating the carrier shaft with respect to the carrier and a clutch unit transmitting a driving force of the paper-transporting roller driving part to the carrier shaft and disposed to be actuated by the carrier which is moved by the carrier driving part when the gap should be adjusted.
The clutch unit includes a clutch part selectively transmitting the driving force of the paper-transporting roller driving part to the carrier shaft, and an actuator actuating the clutch part to transmit the driving force of the paper-transporting roller driving part to the carrier shaft.
The clutch part includes an eccentric rotation gear formed at one end of the carrier shaft and a clutch disposed at the chassis to connect or disconnect the paper-transporting roller driving part to or from the eccentric rotation gear. In this case, it is possible that the carrier ascent/descent part has both ends of the carrier shaft formed of in the form of an eccentric cam which a center axis thereof is eccentrically positioned as much as a given amount with respect to a center axis of the carrier shaft, supporting bushings formed at the chassis to rotatably support both ends of the carrier shaft to ascend and descend.
The clutch includes a first clutch gear engaged with the paper-transporting roller driving part, a second clutch gear coaxially connected with the first clutch gear and disposed to be movable between a power-connected position engaged with the first clutch gear and the eccentric rotation gear and a power-disconnected position separated from the first clutch gear, and an elastic spring elastically pushing the second clutch gear to be positioned in the power-disconnected position.
The actuator includes a plate-shaped member slidably disposed at the chassis to push the second clutch gear into the power-connected position when pushed by the carrier. The actuator can further have a cushioning member preventing an excessive shock power from acting on the clutch when pushed by the carrier.
Also, the apparatus further includes a stopper member restricting the eccentric rotation gear to rotate between at least two positions. The stopper member includes a projection formed at the chassis to protrude toward the eccentric rotation gear, and two counter-projections formed on a movement path of the projection formed at one side surface of the eccentric rotation gear to be engaged with the projection when the eccentric rotation gear is rotated.